Swiss Renaissance physician, botanist, and alchemist Philippe Theophrastus Bombast von Hohenheim—better known as ‘Paracelsus’—asserted in his pioneering studies on toxicology that dosis sola facit venenum, that is any substance introduced into the human body is potentially harmful in function of the quantity introduced.
Unfortunately, even the much beloved “food of the gods” is not exempt from miraculous exceptions in the toxicological field.
Cacao and its derivatives are undoubtedly a delicious source of human nourishment and sensory satisfaction since the dawn of time. Nevertheless, chocolate and other cacao products are recently causing greater and greater concern among their regular consumers, as they can come out as dietary carriers of a chemical element that can be harmful to human health under chronic exposure: cadmium.
In order to dismiss unjustified scaremongering about cadmium in chocolate, two aspects are taken into account: 1) how cadmium is distributed in nature and along the agri-food chain; 2) what the average exposure to cadmium is through foodstuffs and nutrition.
Facts about cadmium in the agri-food and cocoa chain
⠀• Cadmium is a non-essential metal found in the soil where its presence is a result of a combination of natural and anthropogenic processes.
Natural processes include the weathering of rock, volcanic activity, forest fires, erosion and deposition in soils through flooding events by river sediments, while anthropogenic processes include mining and industrial activities, as well as agricultural practices such as irrigation and fertilisation. It is likely that both natural and anthropogenic sources contribute to the soil cadmium content, with the relative importance of different sources depending on the area.
With an incidence of about 90%, food is the primary source of exposure to cadmium for the non-smoking general population.
⠀• Not all cadmium present in the soil is bioavailable to cacao plants—i.e., readily available for uptake by the roots. While higher levels of total cadmium content imply higher potential for cadmium uptake by cacao trees, high levels of cadmium have been reported in cacao beans growing on soil with relatively low total cadmium content and vice versa.
Bioavailability is influenced by multiple soil properties: pH, organic matter content, soil texture, and mineralogy, cation exchange capacity, electrical conductivity, macro- and micro-nutrient content and the presence of microorganisms. Altering these properties is key to reducing cadmium uptake by the plant.
⠀• The cadmium ion is taken up by the cacao roots through specific and non-specific processes used for ion absorption. It is transported via the xylem to the leaves, and reaches the fruit through the phloem. Generally, cadmium concentration in cacao trees decreases from leaves > pod husks > seed shell > shelled nib. Various factors can affect the process of uptake and partitioning of cadmium within cacao plants, such as the age of the tree or plant nutritional status. There is variability in cadmium content across different genotypes, indicating the possibility of identifying low-accumulating cacao varieties.
⠀• Even if the dietary cadmium absorption in humans is usually low (3-5%), the intrusive mineral is retained in the human kidney and liver with a very long biological half-life, ranging from 10 to 30 years.
⠀• Cadmium can also cause bone demineralization for competing with calcium in its absorption in the human body.
Dietary exposure to cadmium in the European population
In 2012, the European Food Safety Agency (EFSA) published a report named “Cadmium dietary exposure in the European population”.
The report included a scientific assessment released in 2009 by the Panel on Contaminants in the Food Chain (CONTAM)—a pool of toxicologists from EFSA—who evaluated the risks to human health related to the presence of cadmium in foodstuffs. Conclusions to the scientific opinion were:
⠀• Often it is not the food with the highest cadmium levels, but foods that are consumed in larger quantities that have the greatest impact on cadmium dietary exposure.
⠀• The mean dietary exposure for adults across EU countries is between 1.9 and 3.0 μg/kg body weight (b.w.) per week, with vegetarians representing the group with the highest dietary exposure (calculated to be up 5.4 μg/kg b.w. per week) in the overall population.
Although adverse effects on human health are unlikely to occur for an individual exposed at this level, the CONTAM Panel concluded that exposure to cadmium at the population level should be reduced and, in their definitive opinion, they recommended a tolerable weekly intake (TWI) of 2.5 μg/kg body weight in order to ensure a high level of protection for all consumers.
Maximum Levels for Cadmium in cocoa products
Following the latest recommendations provided by the CONTAM panel on the tolerable weekly intake of cadmium in the human diet, the previous Regulation (EC) No 1881/2006 regarding maximum levels of cadmium in foodstuffs was amended in May 2014 as Commission Regulation (EU) No 488/2014.
New maximum levels for cadmium in foodstuffs were established and, for the first time, cocoa products were included as a category.
The EU is not alone in regulating cadmium in chocolate. Limits on cadmium levels in chocolate have also been put in place in the American State of California.
The State of California USA has set maximum levels for cadmium in chocolate products under the Proposition 65 settlement agreement, approved on February 14, 2018. Products that exceed the limits can be sold, but in this case a warning must be put on the label:
There is also active discussion regarding recommended limits for cadmium to be included in the Codex Alimentarius.
The maximum permitted levels of cadmium only relate to finished cocoa products, but controls of cocoa beans are warmly advised as good trade practices.
When translating the cadmium levels in chocolate into levels admitted in cocoa beans, European imports consider:
Buyers need to be able to relate the level of cadmium in the cacao beans with the final product. As cocoa butter contains minimal levels of cadmium, the concentration of cadmium in cocoa mass is similar to that in the cocoa bean.
With knowledge of the percentage of cocoa mass in the final chocolate product, the following equation can be used to estimate the maximum cadmium level in cocoa mass that will allow the chocolate product to comply with the relevant EU thresholds:
For example, in the case of dark chocolate containing 70% of cocoa mass (dry cocoa solids), for which the EU regulation sets a maximum permissible limit of 0.8 mg/kg cadmium in the finished product, the maximum level of cadmium in the cocoa mass will be: 0.8/0.7 = 1.1 mg/kg.
This can be used as an approximation for cadmium levels in cacao beans, assuming that unprocessed cocoa mass would contain similar amount of cadmium as the beans or nibs it originates from. Online tools, such as chocosafe.org, are being developed to perform automatic calculations on EU cadmium levels for different chocolate products:
As there is no accepted sampling strategy for cacao beans traded in the EU, good practice from other similar products would suggest taking 5 one-kg samples from a 60-kg sack, and 10 one-kg samples per 0.5 t for products traded by container.
In comparison to other cacao growing regions of the world, the levels of cadmium in cacao regularly exceed these limits in certain areas of Latin America and the Caribbean (LAC):
Much of the cacao produced in LAC is by smallholder farmers whose livelihoods are particularly vulnerable to the new regulations. Many LAC farmers are involved in the production of fine flavor cacao commonly used for products with high cacao content and in single origin niche products that generally fetch a premium price over mass-produced chocolate for the characteristics linked to the flavors originated by virtue of specific varieties and geographies.
Blending high cadmium content cacao beans with beans from other regions or even countries with a low cadmium content can be an effective short-term solution to ensure that products do not exceed the regulatory limits. However, for some areas this will result in the loss of regional identity and flavor differences that are key to the fine flavor cacao market. For fine flavor cacao that cannot be blended, a detailed traceability mechanism of cadmium levels may allow for separation of grains prior to fermentation.
There is a pressing need to find short-, mid-, and long-term solutions to address the issue.
Best practices to ameliorate cadmium uptake at the origin
What’s the state of the current measures investigated to minimize cadmium absorption from soil to plant?
The European Cocoa Association (ECA) and Bioversity International respectively provide in their “Cocoa And Chocolate Industry Requirements” and “Cadmium in Cacao from Latin America and the Caribbean” some useful advice to mitigate cadmium uptake at the origin:
⠀• Increase soil pH, for example by liming, to reduce the availability of Cd. Some ions can influence cadmium uptake directly through competition for soil exchange sites, and chelation or complexation with cadmium compounds. In particular:
⠀⠀◦ Zinc: cadmium and zinc share very similar chemical properties, and this has led to the conclusion that a relative deficiency in zinc in the soil may lead to increased cadmium uptake as they compete for the same transport membranes. Also, it appears that the ratio of cadmium to zinc in soils is normally 1:200-500. Soils with lower ratios than this may therefore exhibit high cadmium accumulation by crops.
⠀⠀◦ Silica: Silica (silicon dioxide) is known to reduce soil cadmium bioavailability as well as its uptake and movement within plants. A source commonly used as a cost effective and efficient filter for contaminated water is diatomaceous earth or diatomite. Diatomite can be incorporated into soils to reduce soil cadmium bioavailability, as pot trials in Peru have shown at applications of over 5%.
⠀⠀◦ Calcium: calcium ions have a very similar ionic radius to cadmium ions, so calcium mitigation can effectively compete against cadmium in root mineral uptake.
⠀• Only use phosphate fertilizers and/or manure which has been checked to ensure it does not contain high Cd levels.
⠀• In areas where soil levels of Cd are high, remove pruned material and pod husks from the ground since these could contain Cd which will be released into the top layers of the soil when they decay.
⠀• Avoid irrigation with Cd-contaminated water.
⠀• Test for deficiencies of nutrients that can compete with Cd absorption.
⠀• Develop and promote utilization of cocoa varieties or rootstocks with low Cd accumulation.
The age of a tree also may influence its uptake of cadmium. Researches indicate that young cacao plants absorb more cadmium than older ones. Among possible explanations for this are that older trees have deeper roots than younger trees, tapping into the sub-soil which contains less cadmium than top-soil. Furthermore, the higher biomass of older trees reduces cadmium concentration through a longer partition from roots to seeds.
Future agronomic research will likely consolidate the indications on the mitigation of cadmium currently available for cocoa farming.
As a chocolate maker/brand, how are you dealing with the maximum limits of cadmium required for cacao products?